Can cheating stabilize allorecognition? Experimental evidence in fungi
Author(s): Bastiaans, E, Debets, AJM, Aanen, DK
Multicellularity is a highly cooperative state prone to invasion by cheating genotypes that use the resources provided by the multicellular organism without contributing their fair share to non-reproductive functions of the organism (e.g. cancers). Kin selection, often realised through regular single-celled bottlenecks (and in some organisms by an early germline separation), is a solution to protect against cheating. In fungi, the lack of an early germline separation and the potential to fuse with other individuals make cheating a realistic threat. However a genetic allorecognition mechanism that limits fusion to almost only clonally related individuals, seems to effectively protect fungi against cheating genotypes. We have shown earlier that in the absence of cheating genotypes, the fitness advantage of fusion selects against allotype diversity in the fungus Neurospora crassa. Individuals with more common allotypes have a higher fitness because they fuse more frequently and gain a larger average size. Studies that model evolution of allorecognition in fungi show that cheating can cause a stable polymorphism for genetic allorecognition loci. Using cheating genotypes generated during an experimental evolution experiment, we empirically test the hypothesis that genetic allorecognition in fungi can be stabilized by the presence of cheating.
Haplodiploidy and the evolution of eusociality: worker revolution
Author(s): Alpedrinha, J, Gardner, A, West, S
Hamilton suggested that haplodiploidy predisposes species to the evolution of eusociality. This is because haplodiploidy increases the genetic similarity of sisters above that of mother and daughter, which could potentially favour an individual to give up her own future reproductive success in order to devote her life to sib-rearing. Trivers and Hare noted that, in order for this to work, helpers need to direct their altruism preferentially towards sisters rather than brothers. Building upon this idea, they proposed two biological scenarios whereby haplodiploidy could promote eusociality: (a) workers biasing the sex allocation of the queen’s brood towards females; and (b) workers replacing the queen’s sons with their own sons. However, biased sex allocation and worker reproduction can have multiple consequences for both the genetic structure of colonies and the reproductive values of males and females. Here we determine the net effect of all these consequences, for the two scenarios whereby the workers seize control of reproduction. We find that: (1) worker control of sex allocation may promote helping, but this effect is likely to be weak and short-lived; and (2) worker reproduction tends to inhibit rather than promote helping.